Hey everyone. I have searched. I was a previous supra owner, so I could basically do any mods and not worry about boost creep issues. I have had my FD since august, and bought it with a blown motor. I know have a reman I got from fritz flynn with 500 miles on it and I want it to last of course. the motor is almost ready to be installed in my car. Here is my mod list:

stock intake
hks carbon ti, DP
gutted cat.
stock IC

Now, I have removed emissions on the vehicle including the ACV. Since the ACV is removed, the airpump will not be functioning. with that being the case, i don't want the cat to be there to burn up, that is the reason for wanting to gut it. HOWEVER, gutting it with the DP and CB have me worried about boost creep to the point where I am thinking I should just put the ACV back on. Does anyone have thoughts on this? I understand all cars are different, and some will creep and some won't as I found in my search, but does this throw up very obvious red flags to everyone? Or, can I just go gutless on the cat with those mods and port the wastegate and be satisfied?

Trev

 

Are you going for power, reliability, low cost, ??

I would leave that stock cat in there and cap off the air injection pipe. (Actually, since I personally wouldn't drive a massive smog machine on a daily basis, I'd put the air pump back in). But if you don't care about emissions, leave the cat in. The stock cat will burn up and clog a little faster, but since it sounds like you're trying to keep it simple I would probably skip it for now. You can always drop the cat and gut it if it seems to be running really hot or your boost starts to get weak.

Even if you gut the stock cat, the stock intake, stock intercooler, and stock cat piping will probably be enough restriction that you won't see boost creep. But you will most likely need a boost controller to get your boost down to 10psi again. (you didn't say what ecu you were running, but if it's a stock ecu you'll need to wind back down to 10psi after installing these flow mods).

 

I am going for reliability with decent power. I will eventually put on a PFC.
running stock ECU and using 2 ball/spring manual valves for boost control..

Trev

 

ttt

 

Then I would leave the stock cat, set your boost to 10psi. While I tend to think you won't have enough flow to see boost creep, gutting the cat is more likely to see creep than if you leave it as-is.

Dave

 

then I will need to put the ACV back on so I can run the air pump...what about this...

do I need an airpump to run a high flow cat? Will the aftermarket high flow clog without the airpump?

Trev

 

I ran a Bonez hi-flo without an airpump for a while. The cat looked just fine when I took it off and sold it. I haven't seen anyone who has been able to directly relate a fail cat to not running an airpump. Your exhaust will not be as clean, that is for sure, without the airpump.

 

So, to clarify, if I run a stock IC, stock intake, CB, MP, DP, and I port the wastegate, would that greatly reduce the risk of boost creep. I am also not too excited about having the exhaust reeking either

Trev

 

Porting the wastegate is an option, but as mentioned, may not solve the problem completely. Another attempt at controlling boost creep is using exhaust restriction plates. That ends up being a more configurable fix as you can play with the proper restriction size for your car.


Now, not every car experiences boost creep. Some do, some don't for whatever reason.

 

I wonder if it's not so much that certain cars experience boost creep and some don't as it is different climates are was have an effect?

 

Yes, that is part of it as well. There are many factors that come into play, but there is no single one or combination of ones which would help determine which cars are more likely to experience creep and which ones aren't.

 

I have not heard of more than a couple of cases where porting the wg does not stop creep, and in those cases they simply hadn't ported quite as large as they could have.

Do you have more info on that?

Dave

 

If you are going to port the wastegate, I say just drop a midpipe in. The stock IC/intake will further help in keeping creep in check. Worst comes to worst, you will have to install a restrictor plate at the midpipe, which isn't a big deal.

If you do this, you will have to verify come winter time that your boost is still holding at 10 psi. You may have to play with the boost controller to reduce spiking at the transition also.

 

heck, I won't even be racing this car, running over stock boost, or driving it between october through april....I should just midpipe it, keep stock intake and stock IC and run the DP, MP, CB and stock boost. I will be running 2 ball/spring boost control valves and have all my reliability mods to boot...is there a turbulence benefit for going with a straight midpipe instead of gutting the cat?

Trev

 

BTW, a cat is probably the only way to keep the smell down, isn't it?

 

Of course, and the significant increase in diameter of pipe helps too.

I have a streetport with all bolt-ons and BNRs (ported wastegate) and have no problem holding 10 psi in temps above 50F.

 

so you are saying a midpipe is the better coice over the gutted cat, correct? Will one be better on boost creep than the other because of the diameters?

Trev

 

Of course a midpipe flows better than a gutted cat. The gutted cat will create less of a boost creep issue, but what I'm saying is that with a ported wastegate, you shouldn't have boost creep issues.

 

Rynberg, so you are saying that with the stock intake/stock IC, CB, gutted cat, DP, you would still advise to definately port the wastegate?

Mahjik is saying that I can run the cat(normal, ungutted), and actually still use the airpump with the ACV removed...I have thought about that so my exhaust doesn't smell so bad as well...

Trev

 

ttt

 

If you can afford to get a PFC and get it mapped, you wont need to port the wastegate.

my car is stock except bigger intercooler, feed downpipe, decat centre section and all emissions removed along with a cat back. Runs 14psi fine all day long, no creep.

 

Just some clarifications on this:

1. The PFC does not eliminate creep.

Creep as mentioned earlier can come into play in different configurations. In the above example, he may creep to 14 PSI trying to keep the boost at 12 PSI. However, if he just runs 14 PSI, he's not noticing any creep.

Now, I'm not saying he has boost creep and doesn't know it, I'm throwing out an example of boost creep being subjective. Most people run into boost creep trying to keep the car in those in between boost numbers like 11-13 PSI.

So, how can the PFC help? If you know you are creeping to 15 PSI, get the car tuned for 15 PSI. However, its still the best idea to be able to control the boost to whatever setting(s) you want to run. If you want to run at 10, 12 or 13 PSI your boost should be able to be controlled to do so.

 

good points mahjik. Apologies, i was feeling lazy when i replied, my answer was half assed.

basically if you get a PFC you can tune the car with increased boost so that the exhaust gas that normally causes the boost creep is now used to generate boost pressure instead, so there is no excess and no creep.

getting a PFC will NOT allow you to magically run 10psi again if your car is boost creeping now.